[XrdCl] Use threads by default in posix aio.

src/XrdCl/XrdClConstants.hh

@@ -68,7 +68,7 @@ namespace XrdCl
   const int DefaultLocalMetalinkFile    = 0;
   const int DefaultXCpBlockSize         = 134217728; // DefaultCPChunkSize * DefaultCPParallelChunks * 2
   const int DefaultNoDelay              = 1;
-  const int DefaultAioSignal            = 1;
+  const int DefaultAioSignal            = 0;
   const int DefaultPreferIPv4           = 0;
 
   const char * const DefaultPollerPreference   = "built-in";